During playing gold there are many occasions where a golf player wants to know a distance from a starting point to a pin in the hole on a target green.
For this purpose, various optical and acoustic devices of simple construction have hitherto been commercially available for measuring a distance (for example, Japanese U.M. Publication No. 2688/78, Japanese Opened U.M. Application Nos. 27706/83, 139170/83, 133271/84, and Japanese Patent Publication No. 39306/83).
In a conventional method for measuring a distance with such known devices, points A and B for measuring an angle are established in such a way that they are spaced apart by a distance L from each other for locating a measuring point M therebetween, as shown in FIG. 4, in order to actually measure the angle formed between the lines A-M and A-P, wherein P represents a point to be measured, as well as an angle formed between the lines B-M and B-P, thereby to make an equal angle .theta.. Thus, a distance X from the measuring point M to the point P to be measured may be calculatd from the following equation: EQU X=L tan .theta.
Such procedure has also being utilized in a system for a camera view-finder to align a vertically separated image to the center, thereby bringing focus into the distance.
In such a case, however, a large proportion of the distance 2L between the points A and B relative to the distance X makes an angle .theta. of approximately 90 degrees, so that the value of tan .theta. approaches to infinity, thus, introducing a large error in the measured distance X.
For this reason, when measuring a distance even on a golf course of a usual distance shorter than 300 m, a distance 2L of 20 to 30 cm is required to bring the measured error less than 1%. As a result, a 20-30 centimeters long element for establishing the angle-measuring points A and B is required, which is inconvenient to carry during playing golf and hence has not been a popular commercial product.
Accordingly, an object of the invention is to solve the above problems and to provide a method for measuring an accurate distance instantaneously and conveniently by means of a compact device using a quite different system from the conventional methods.